Late Quaternary Pedogenesis of Lacustrine Terraces in Gallocanta
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Document downloaded from: http://hdl.handle.net/10459.1/65090 The final publication is available at: https://doi.org/10.1016/j.catena.2016.07.046 Copyright cc-by-nc-nd, (c) Elsevier, 2016 Està subjecte a una llicència de Reconeixement-NoComercial- SenseObraDerivada 4.0 de Creative Commons CATENA 147: 372–385 (2016) http://dx.doi.org/10.1016/j.catena.2016.07.046 1 Late Quaternary pedogenesis of lacustrine terraces in 2 Gallocanta Lake, NE Spain 3 E. Luna a,*, C. Castañeda a, F.J. Gracia b, R. Rodríguez-Ochoa c 4 a Estación Experimental de Aula Dei, EEAD-CSIC, Av. Montañana 1005, 50059 Zaragoza, 5 Spain 6 b Departamento de Ciencias de la Tierra, Universidad de Cádiz, 11510 Puerto Real, Cádiz, Spain 7 c Departamento de Medio Ambiente y Ciencias del Suelo, Universitat de Lleida, Av. Rovira 8 Roure 191, 25198 Lleida, Spain 9 *Corresponding author. E-mail address: [email protected] (E. Luna). 10 11 Abstract 12 Transitional areas of lake margins are complex environments whose evolution is strongly 13 controlled by flooding frequency and persistence. The edaphic development of lacustrine 14 marginal environments can be reconstructed by combining detailed geomorphological analysis 15 with a systematic edaphic study of toposequences. This approach has been applied to a set of 16 recent lacustrine terraces in the downwind palustrine area of the Gallocanta saline lake, located 17 in a semiarid area in NE Spain. Up to five terraces, from 1.6 to 4.5 m above the lake bottom, 18 have been identified and mapped using stereo photointerpretation and airborne LiDAR data. 19 Several cycles of water level fluctuations, as part of a general trend towards lake desiccation, 20 have generated stepped terrace levels. The soils of these terraces have different morphological 21 characteristics and provide evidences for the Gallocanta paleolake being larger than that of the 22 present day. The soils have a sandy loam texture with variable clay content (1% to 46%) and a 23 predominantly carbonate composition (mean = 26%). The soils are developed in a sequence of 24 lacustrine carbonate-rich (mean = 37%) fine-grained gray layers overlaying detrital (mean = 51% CATENA 147: 372–385 (2016) http://dx.doi.org/10.1016/j.catena.2016.07.046 25 gravels) and frequently erosive, carbonate-poor reddish layers. The pedogenesis of the 26 downwind palustrine area is mainly characterized by poorly-developed carbonate accumulations 27 and common redox mottles associated with water level fluctuations in the lake, which 28 continuously rejuvenate or truncate the soils. Integrating pedological and geomorphological 29 features provides insight into recent complex lacustrine and soil forming processes and facilitates 30 management strategies and plans for this protected saline environment. 31 1. Introduction 32 Little is known about wetland soils developed in lake basins under semiarid climates. These soils 33 frequently become seasonally or intermittently dry due to the limited precipitation and high 34 evapotranspiration rates. Along the margins of arid wetlands, soil formation and properties are 35 closely related to geomorphic position and fluctuations in lake, or playa-lake, water levels 36 (Kolka and Thompson, 2007; Biggs et al., 2010; Farpoor et al., 2012; Shabanova et al., 2015). 37 For this reason the study of wetland soils is always intimately linked to the study of wetland 38 geomorphology and hydrology (Richardson et al., 2001). 39 Lake margins in semiarid climates are complex environments where sedimentation and soil 40 formation are determined by the balance between detrital inputs during wet seasons and salt 41 deposition during dry conditions (Boettinger and Richardson, 2001). In the wetting-drying 42 margins of the lake, water action on soils strongly influences their characteristics such as texture, 43 color, and types of horizons (Richardson et al., 2001). In this context, the study of soils provides 44 evidence of recent and past water level fluctuations in the lake (Castañeda et al., 2015), and may 45 be used for identifying regulatory boundaries (Lichvar et al., 2006). If high lake water periods 46 are long enough, they favor the generation of a morphosedimentary marginal surface of mixed 47 sedimentary-edaphic origin which can be abandoned and left perched once the lake level drops 48 again (Romanovsky, 2002). This is the origin of stepped lacustrine terraces in lakes that 49 experience a progressive desiccation trend (Gracia, 1995; Landmann and Reimer, 1996), as is the CATENA 147: 372–385 (2016) http://dx.doi.org/10.1016/j.catena.2016.07.046 50 case of Gallocanta Lake. Water level fluctuations in lakes are common in the arid and semiarid 51 Mediterranean region where most lakes are shallower (Beklioglu et al., 2007) and more sensitive 52 to climate oscillations than in more humid areas. Lake water level fluctuations during the Late 53 Quaternary have received much attention as proxies for identifying past environmental changes, 54 usually based on sedimentology (Ghinassi et al., 2012; De Cort et al., 2013; McGlue et al., 2013) 55 together with paleoecological evidence (e.g., pollen, ostracods, diatoms) (Shuman et al., 2001; 56 Hoffmann et al., 2012). 57 Although classic geomorphological studies of lakes focus on the different lake morphologies in 58 order to understand their origin and general evolution (Timms, 1992), few studies have 59 investigated the geomorphology of lacustrine terraces in shallow lakes and most of these studies 60 have looked at Pleistocene terraces related to major climatic oscillations (Bowman, 1971; Stine, 61 1990; Abu and Kempe, 2009; Ocakoglu et al., 2013). Only isolated contributions relate the 62 distribution and elevation of Holocene lacustrine terraces to recent climate changes 63 (Romanovsky, 2002; Gutiérrez et al., 2013). In fact, when compared to Pleistocene terraces, 64 Holocene historical levels are usually close to present water levels and hence their study requires 65 a very detailed high-resolution topographic analysis to distinguish different historical and recent 66 terrace levels, not often affected by present flooding. 67 Recognition of such lacustrine terraces and associated past flooding events requires 68 geomorphological and topographical techniques. Hence, lake terrace formation and the 69 interaction between lacustrine and pedogenetic processes can be reconstructed by combining 70 detailed geomorphological analysis and a systematic edaphic study of toposequences. This kind 71 of quantitative analysis is feasible with modern topographic techniques like airborne LiDAR 72 surveys and the digital terrain models derived from them, together with GIS software (Jones et 73 al., 2008; Budja and Mlekuž, 2010). High-resolution LiDAR-derived digital elevation models CATENA 147: 372–385 (2016) http://dx.doi.org/10.1016/j.catena.2016.07.046 74 have been widely applied in coastal areas (Kim et al., 2013; Matsu’ura, 2015) and fluvial 75 systems with subtle topography (Jones et al., 2008). 76 The present study focuses on soil development in lacustrine terraces that are assumed to have 77 been intermittently exposed during Late Quaternary-historical times, in the Gallocanta saline 78 lake, NE Spain. The aim is to integrate pedological and geomorphological features to reconstruct 79 the lacustrine terraces formation and understand recent lacustrine and soil formation processes 80 associated with water level fluctuations. 81 82 2. Gallocanta Lake 83 2.1. General setting 84 Gallocanta Lake is the largest well-preserved saline lake in Western Europe and has been 85 included in the Ramsar list since 1994 (Ramsar Convention Secretariat, 2010). The area 86 comprises a 6477 ha natural reserve that is protected and managed by the local government in 87 order to conserve endemism as well as habitats for the overwintering of migratory birds (Leránoz 88 and González, 2009). The lake, formed at the bottom of a karst polje (Gracia et al., 2002), is 89 located in a 543 km2 endorheic basin at approximately 1000 m.a.s.l. in the Iberian Chain, NE 90 Spain. The basin holds more than 20 lakes of karstic origin, Gallocanta Lake being the largest. 91 The Gallocanta Quaternary basin is elongated in the dominant wind direction (NW-SE), parallel 92 with the Valdelacasa mountain range, which runs along the NE side of the basin with peaks of up 93 to 1400 m.a.s.l. (Figure 1). This mountain range is composed of siliceous Ordovician rocks and 94 flanks an extensive outcrop of deformed carbonate units from the Mesozoic (Gracia, 2014). The 95 basin is excavated into Triassic clays and gypsum, as well as other more soluble salts (Gracia, 96 2009) which contribute to the soil and water salinity. The center of the lake contains about 1 m 97 of lacustrine sediments, the oldest of which have been dated as 43 ky BP (Rodó, 1997). Sediment CATENA 147: 372–385 (2016) http://dx.doi.org/10.1016/j.catena.2016.07.046 98 cores were analyzed for reconstructing Late Quaternary paleoenvironmental and paleoclimatic 99 changes by Schütt (1998), Rodó et al. (2002) and Luzón et al. (2007), as well as other authors. 100 The climate is dry semiarid (Liso and Ascaso, 1969) and there is a large yearly variation in 101 rainfall; the mean annual precipitation over the last 70 years is 488 mm yr-1 (range = 791 mm in 102 1959 to 232 mm in 2001), and the mean annual temperature is 11.3 °C for the period 1969-2012. 103 The frequent NW winds (Figure 1) exacerbate the hydric deficit (Martínez-Cob et al., 2010) and 104 produce longshore currents to the SE, generating shoreline landforms similar to those of marine 105 coasts (Castañeda et al., 2013). Water level fluctuations constitute the most outstanding feature 106 of the lake. The maximum lake water level, 2.84 m, was registered in 1974 (Pérez-Bujarrabal, 107 2014) and the lake desiccates completely during periods of low rainfall.